Japanese Submarines – Critical operational life and hull cutting issues

"In 1994 the RAN Magnetic Treatment Facility (MTF) was commissioned into service following the successful deperm [demagnetising] of the Oberon Submarine HMAS Orion. Since then the MTF has been used to successfully deperm several other classes of vessels including a Collins Class submarine, ANZAC Frigate, Fremantle class Patrol boat and a decommissioned Hydrographic ship." (Description above "Executive Summary" page 1. Photo courtesy Page 3 http://dspace.dsto.defence.gov.au/dspace/bitstream/1947/4085/1/DSTO-TR-1340%20PR.pdf)

---

In comments below http://gentleseas.blogspot.com.au/2015/08/australias-naval-shipbuilding-blueprint.html “S” (and comment at August 8, 2015 at 7:47 PM for answeres to 2.1 and 2.2) has provided very interesting views on Japanese-Australia submarine issues. This is concerning the Soryu and Collins.

The actual submarine designs that are being proposed for SEA 1000 will be significantly different from current subs - but discussion has more substance when on the basis of current subs. The Japanese proposal, which will likely win the SEA 1000 CEP, is likely to be an evolution of the Soryu.

One concern is that the operational period of postwar Japanese submarines, including the Soryu is significantly shorter than the 30 year average for submarines designed in Europe or the US.

I have clarified the English in S’s responses and hope this clarification is faithful to his intended meaning. On August 5, 2015 S indicated:

That he thought that having set views on average years of operation of a submarine without considering the rate of operation is “meaningless.”

“Submarine hull will experience physical, chemical and chemical-physical degradations such as fatigue, corrosion and stress-corrosion cracking. Also, mechanical parts such as diesel engines, batteries systems and AIP systems will deteriorate. These degradations will come up only under actual operational conditions. For example, if there is no repeated surfacing-submerging, the fatigue of the hull caused by repeated application and release of external stress is not experienced.

It is said that the rate of operation of the Soryu submarine is 80%. As operational period of Soryu is 24 years, actual operation period becomes ca. 19 years (= 24 years x 0.8). In the case of the Collins submarine, the rate of operation is obviously lower than that of the Soryu. For the Collins’ 60% operational rate over a 30 year operational period, the actual operational period becomes 18 years (= 30 years x 0.6) which is nearly same as that of Soryu.

[Best to consider the] increase in numbers of submarines [and] also improvements in the rate of operation.”

On August 6 I asked S five questions – and below each I have provided S’s responses, also provided on August 6. I have added follow-up questions in bolded italics.

1. Why is the "operational period of Soryu 24 years"?

S answered “Submarine operational periods used to be as short as 18 years, and JMSDF [Japanese Navy] was criticized. Also National Defense Program Outline FY 2011 decided to increase number of submarine to 24 including 2 training submarines.”

The previous JMSDF requirement and orbat was 16 submarines. Japanese perceptions of an increased threat from China (and perhaps some US persuasion) has resulted in the revision upwards to 24 subs.

2. Why not 30 years like Germany, France and almost all other submarine builders?

S answered “Submarine building span in Japan is in line with Long-term or Mid-term Defense Buildup Plan and technology innovation.”

So are the following factors important in the number of years of operational life for a Japanese submarine?:

2.1  Is there a need for continuous build by KHI/MHI?

 (The pattern of launching and commissioning one submarine per year appears to be very important. Continuous build would keep the workers (eg. welders) busy and would make budgeting more certain for the JMD and KHI-MHI.)

S answered "I think that the continuous building system is an implicit requirement to achieve and maintain a higher performance [capability] of the Japanese submarine force [and individual subs]. One of the most important technologies is hull welding. Welders must be continuously engaged in welding to maintain their welding skill and qualifications, especially for gas tungsten arc welding (GATW). Other technicians, including inspectors, must maintain skills and qualifications. Inspectors are required to have the highest skill." 

2.2 I have a theory that the reason the Yield Strength of the pressure hull steel is very high (at NS110 = HY156 see Submarine Pressure Hull Table) is due to deep diving needs. So does deep diving put greater stress on the pressure hull – leading to more rapid degradation – resulting in shorter operational life?

S answered: "[The relationship] between operational life and hull strength is not clear, because operational life of Uzushio class submarine [see SS-566] with NS63 hull was 18 years."

"I think Australia should not persist [with] NS110 technology [use Japanese NS110 grade steel for the] following reasons: 

1) this technology including GTAW technology is one of most important technology which Japan cannot share with other countries (eg. Germany does not share its non-magnetic hull steel, except with Italy [the joint builder of the 212]), 

2) maintenance of this technology is very difficult [particularly cutting and welding], 

3) new steel which Japan will propose may be more suitable for Australia than NS110."

"I think that Collins class with single hull made of BIS 812 EMA [see Submarine Pressure Hull Table] is out of date in terms of magnetism. As the Ni content (1.28wt%) of BIS 812 EMA is very low [1], this steel is magnetic. So a weak point of the Collins class is a more detectable hull than more modern submarines (which have a low magnetic single hull or low magnetic double hull (low/non-magnetic outer hull and magnetic inner pressure hull)). [On BIS 812 EMA's Ni content see page 11 and much detail on BIS 812 EMA's magnetic properties in that document - including pages 24-25. Many references to magnetism and submarines here.  So development of welding user friendly steel with higher Ni and Cr contents improving magnetism and low-temperature properties is a better option."

3. What happens if Australia needs to lift availability of its Japanese built submarine to 80% in time of strategic need?

S answered “I think that Australia may reduce defense cost as a result of reduction in number of submarines.”

4. What happens if Australia wants to cut the NS110 pressure hull and reweld it to do major maintenance work (including large parts replacement on the propulsion system) or major emergency repairs?

S answered along the lines: Hull cutting significantly weakens the pressure hull thus limiting diving depth. [JDS Asashio (see SS-589 converted to testbed submarine TSS-3601 preceded Oyashio Class has an NS110 and NS80 pressure hull like Soryu Class) required hull-cutting for the experimental fitting of the large Stirling AIP system. After this hull-cutting the submerged depth of Asashio was limited.]

5. Can this pressure hull cutting-rewelding work be done in Australia?

[see S's answers to 2.2 above] “Aside” [this depends?] “whether JMSDF agrees NS110 technology transfer or not, advise from Japan is required, because Japan has an experience of hull-cutting of [the NS110 and NS80 pressure hull for the] “Asashio”.

S made the observation "I think there are four options for Australia's of next submarine: 1) modified SS29 [or 29SS see see Table at bottom of] type of Japan, 2) modified SS29 type with new steel hull, 3) Type 216, 4) Conventional "Shortfin" Barracuda."

Thankyou S.

Please connect with previous Submarine Matters articles, including:

Technical Problems: Fuel Cell AIP and Hull Cutting of June 25, 2015, and

Major Soryu hull life issue? – Maintenance/Emergency Welding in Japan only? Of June 5, 2015.

Pete